The present invention relates to a method for operating an internal combustion engine, in particular a motor vehicle, in which fuel is injected directly into a combustion chamber either in a first mode during a compression phase or in a second mode during an intake phase, and in which the fuel quantity injected into the combustion chamber is subjected to control and/or feedback control in differing ways in the two modes. In addition, the present invention relates to an internal combustion engine, in particular a motor vehicle, having an injection valve, using which fuel can be injected directly into a combustion chamber either in a first mode during an intake phase or in a second mode during a compression phase, and having a control unit for the differing control and/or feedback control of the fuel quantity injected into the combustion chamber in the two modes.
Conventional systems directly inject fuel into the combustion chamber of an internal combustion engine. In this context, the distinction is made between so-called stratified operation, as the first mode, and so-called homogeneous operation, as the second mode. Stratified operation is used, in particular, in the case of smaller loads, whereas homogeneous operation is used in the case of larger loads placed on the internal combustion engine.
In stratified operation, the fuel during the compression phase of the internal combustion engine is injected into the combustion chamber such that at the moment of ignition, a fuel cloud is located in the immediate vicinity of a spark plug. This injection can take place in different ways. Thus, it is possible that the injected fuel cloud is located at the spark plug during or directly after the injection and is ignited by the spark plug. Likewise, it is possible that the injected fuel cloud is directed to the spark plug by a movement of the charge and is only then ignited. In both combustion methods, there is no even distribution of the fuel but rather a stratified charge.
The advantage of the stratified operation lies in the fact that using a very small quantity of fuel the smaller loads applied can be handled by the internal combustion engine. Larger loads, on the other hand, can not be handled by the stratified operation.
In homogeneous operation, which is provided for larger loads of this type, the fuel is injected during the intake phase of the internal combustion engine so that a swirl effect and thus a distribution of the fuel in the combustion chamber can take place without difficulty. To this extent, the homogeneous operation roughly corresponds to the mode of internal combustion engines in which fuel is injected into the intake pipe in the conventional manner. If necessary, homogeneous operation can also be employed with smaller loads.
In stratified operation, the throttle valve in the intake pipe leading to the combustion chamber is opened wide and the combustion is controlled and/or feedback controlled only by the fuel quantity to be injected. In homogeneous operation, the throttle valve is opened or closed as a function of the torque requested and the fuel quantity to be injected is controlled and/or feedback controlled as a function of the quantity of air taken in.
In both modes, i.e., in stratified operation and in homogeneous operation, the fuel quantity to be injected is controlled and/or feedback controlled as a function, additionally, of a plurality of further input variables with respect to an optimal value regarding fuel economy, emissions reduction, and the like. The control and/or feedback control, in this context, is different in the two modes.
It is necessary to switch the internal combustion engine from stratified operation to homogeneous operation and back again. In stratified operation, the throttle valve is opened wide and the air is therefore supplied in a largely unthrottled (unimpeded) manner. In the homogeneous operation, the throttle valve is only partially opened thus limiting the supply of air. Above all, in the switchover from stratified to homogeneous operation, the capacity to accumulate air in the intake pipe leading to the combustion chamber must be taken into account. If this is not taken into account, the switchover can lead to an increase in the torque generated by the internal combustion engine.
A Summary objective of the present invention is to provide a method for operating an internal combustion engine using which an optimal switchover is possible between the two modes. This object is achieved according to the present invention in that a switchover takes place from the first mode initially to transitional operation of the second mode and then to normal operation of the second mode.
Thus the switchover does not occur immediately to homogeneous operation, i.e., to a stoichiometric or rich air/fuel mixture, but rather the internal combustion engine is first operated in a transitional operation of the homogeneous operation. As a result of this transitional operation, it is achieved that the entire switchover procedure from stratified operation to homogeneous operation leads to a significantly lower increase of the torque generated by the internal combustion engine. Therefore, there is a significantly smaller excess torque that has to be eliminated for example by a retarded (late) setting of the ignition angle. This not only represents marked fuel economy, but also, as a result of the reduced retarded setting of the ignition angle, the possibility of changes in the torque generated by the internal combustion engine is significantly reduced. Therefore, disruptions have only diminished influence on the smooth running of the internal combustion engine. Furthermore, as a result of the reduced retarded setting of the ignition angle, a reduced increase in the emission temperature is achieved, which is also advantageous for the smooth running of the internal combustion engine and for its service life.
In an example embodiments of the present invention, the air quantity supplied is measured, and a switchover occurs from the first mode to the transitional operation of the second mode as a function of the air quantity supplied, specifically after the air quantity supplied sinks below a first threshold value, or a switchover occurs from the transitional operation of the second mode to the normal operation of the second mode as a function of the air quantity supplied, specifically after the air quantity supplied sinks below a second threshold value.
The switchover procedures are therefore carried out as a function of the air quantity supplied. The air quantity supplied can, be measured, for example, with the assistance of a mass airflow sensor. Then, if necessary as a function of the rotational speed of the internal combustion engine and/or other parameters, the two threshold values for the switchover procedures are determined. If the air quantity accumulating in the intake pipe is reduced, then the level initially sinks below the first threshold value. Thereupon, the internal combustion engine is switched over from stratified operation to the transitional operation of homogeneous operation. The air quantity accumulating in the intake pipe is reduced further and then sinks below the second threshold value. The internal combustion engine is then switched over from the transitional operation to the normal operation of homogeneous operation. The dependence of the switchover procedures on the air quantity supplied represents, in this context, a particularly simple and precise way of carrying out the entire switchover of the internal combustion engine from stratified operation to homogeneous operation.
In an advantageous embodiment of the present invention, in the transitional operation of the second mode, the fuel/air mixture supplied is controlled and/or feedback controlled in accordance with a somewhat leaner value. The transitional operation of the homogeneous operation is therefore a leaner homogeneous operation or a homogeneous leaner operation having a leaner air/fuel ratio. The fuel/air mixture therefore has a value greater than 1.
In this context, it is particularly advantageous if, after the switchover from the first mode to the transitional operation of the second mode, the fuel quantity to be injected is determined on the basis of the air quantity supplied and the torque requested. This represents a simple and precise way of realizing the leaner homogeneous operation.
Furthermore, it is particularly advantageous if, after the switchover from the first mode to the transitional operation of the second mode, the ignition angle is determined on the basis of the air quantity supplied, the fuel quantity injected, and the torque requested. Thus the requested torque can be generated simply and precisely during leaner homogeneous operation.
In a further advantageous embodiment of the present invention, in the normal operation of the second mode, the fuel/air mixture supplied is controlled and/or feedback controlled in accordance with a preselected, in particular stoichiometric value. The fuel/air mixture therefore has a defined, preselected value, for example 1. In this way, a particularly low-emission operation of the internal combustion engine is achieved.
In this context, it is particularly advantageous if, after the switchover from the transitional operation to the normal operation of the second mode, the fuel quantity to be injected is determined on the basis of the air quantity supplied. In this manner, it can be assured that the preselected or stoichiometric value of the fuel/air mixture is maintained.
Furthermore, it is may be advantages; if, after the switchover from the transitional operation to the normal operation of the second mode, the ignition angle is determined on the basis of the torque requested. Using the ignition angle, particularly short-lasting changes in the torque can be achieved in this way, without having to change the preselected or stoichiometric value.
The method according to the present invention may be realized in the form of a control element, which is provided for a control unit of an internal combustion engine, in particular a motor vehicle. In this context, a program is stored in the control element that is executable in a computing device, in particular in a microprocessor, and that is suitable for carrying out the method of the present invention. In this case, the present invention will be thus realized by a program that is stored on the control element so that this control element, which is provided with the program, represents the present invention in the same manner as the method for whose implementation the program is suited. As the control element, specifically an electrical storage medium can be used, for example a read-only memory.
Further features, application possibilities, and advantages of the present invention can be seen from the following description of the exemplary embodiments of the invention, represented in the Figures of the drawing. In this context, all of the features described or depicted, either singly or in any combination, constitute the subject matter of the present invention, irrespective their antecedent reference, and irrespective of their formulation or representation in the description or in the drawing.